The present invention relates to fine-particle, crosslinked bead polymers having a narrow particle size distribution and also to a process for their preparation.
Fine-particle bead polymers having a narrow particle size distribution, based for example on styrene or acrylic esters, are known. The preparation of substantially monodisperse particles of this type is carried out by a complicated 2-step process (Makromol. Chem. 180, (1979), 737; Adv. Coll. Interf. Sci. 13 (1980), 101). Pearl-like polymer particles having a relatively narrow particle size distribution can also be prepared by suspension copolymerization of maleic anhydride and .alpha.-olefins (DE-A-2,501,123, DE-A-2,919,822 and DE-A-3,144,793). Bead like graft copolymers whose grafted-on branches are composed of methacrylic acid/methyl methacrylate and whose graft base is composed of maleic acid/.alpha.-olefins have been disclosed in DE-A-3,331,542. EP-A-80,225 describes a method for the preparation of stable aqueous dispersions by which, for example, styrene bead polymer or methyl methacrylate bead polymer having a narrow particle size distribution can be obtained. DE-A-3,708,032 discloses fluorine-containing bead polymers having an average particle diameter of 0.5-10 .mu.m and a narrow particle size distribution.
Fine particle bead polymers of this type having a narrow particle size distribution are used, among other applications, as matting agents or spacer materials in photographic recording elements. Another field of application is the preparation and processing of films. The bead polymers counteract the sticking together (blocking) of layers of film; they improve the surface slip characteristics and promote higher processing speeds. An important disadvantage of the known polymeric spacer materials is their low heat resistant and low solvent resistance, this greatly limiting their usefulness, particularly in the film field.
There is therefore a need for polymeric spacer materials having improved heat resistance.